1. Field of the Invention
This invention relates to control of pitch in papermaking, and of the compositions useful therefor.
2. Description of the Prior Art
The most efficient prior pitch control agents are sodium salts, especially sodium salts of sulfonated naphthalene-formaldehyde condensate. The aforementioned pitch control agents are anionic which causes them to suffer from the disadvantage that when they are used in a system which contains cationic additives such as cationic wet strength resins, cationic sizing agents, cationic retention aids, cationic drainage aids, cationic dry strength resins, and the like, the anionic pitch control agents react and precipitate the cationic additives. Presently, when the paper system contains a cationic additive, either no pitch control agent is used, or one tries to emulsify the pitch with surfactant, or one uses clay to detackify pitch. Clay is cheap, but one must use large amounts of it to control pitch, often over 1% by weight based on pulp solids; furthermore, and more importantly, clay is a debonding agent and so can weaken the paper sheet, and also the pitch is non-dispersed and so can cause spots in the paper. A non-ionic pitch dispersant is disclosed in Drennen et al, U.S. Pat. No. 3,081,219, but a disadvantage of non-ionic dispersants is that they do not function to retain the pitch in the pulp.
Pitch has become more of a problem in recent years due to the growing tendency of mills to use high yield pulps which are less pure than previously. The pulps are not cooked as long or washed as thoroughly as in previous years, so the paper now contains increased levels of pitch and other anionic pulpwood resins and rosin.
Another cause of increased pitch and other associated sticking problems is closed white water systems which have come into being because of ecological necessity. Another cause of increased pitch problems is the trend to cut logs into chips in the forest rather than at the mill, and so the chips are prepared while the log is still green, causing exuding. Another cause of increased pitch problems is the inclusion of lower grade woods and fresher timber.
A need has arisen for a more efficient pitch control agent which is compatible with cationic wet end additives.
It is an object of the present invention to provide a pitch control agent which is compatible with cationic wet end additives.
A further object is to provide a pitch control additive which functions to disperse pitch and to deposit or retain the dispersed pitch into the pulp in finely divided form.
Another object is to provide a pitch control method which is efficient and does not interfere with the function of other additives.
These objects, and others as will become apparent from the following disclosure, are achieved by the process of the present invention which comprises the utilization of a composition for preventing deposition of pitch comprising a water soluble, linear cationic polymer comprised of units of the formula ##STR2## wherein A is a (C.sub.2 -C.sub.3) alkylene group, R is H or CH.sub.3 ;
R.sup.1 is hydroxyethyl or hydroxypropyl group, PA1 R.sup.2 is a (C.sub.1 -C.sub.4) alkyl group, PA1 R.sup.3 is a (C.sub.1 -C.sub.4) alkyl group, and PA1 X is an anion;
said polymer having a viscosity average molecular weight, M.sub.v, of about 35,000 to 70,000.
In another aspect the invention comprises a process for controlling pitch in papermaking comprising incorporating about 0.01 to 0.5% by weight of said composition in the pulp slurry, said ratio being based on pulp solids.